1. Field of the Invention
The present invention relates to fuel systems for internal combustion engines, and particularly to valves for controlling pressure of fuel delivered to injector valves in the engine.
2. Description of the Related Art
For many decades gasoline internal combustion engines used a carburetor to mix fuel with incoming air. The resulting air/fuel mixture was distributed through an intake manifold and mechanical intake valves to each of the engine cylinders. Multi-port fuel injection systems have replaced the carburetion systems for most engines. A multi-port fuel injection system has a separate fuel injector valve which injects gasoline under pressure into the intake port at each cylinder where the gasoline mixes with air flowing into the cylinder. Even with multi-port fuel injection, there are limits to the fuel supply response and combustion control which can be achieved.
More recently a third approach to supplying fuel into the engine cylinders has been devised. Known as xe2x80x9cgasoline direct injectionxe2x80x9d or xe2x80x9cGDIxe2x80x9d, this techniques injects the fuel directly into the combustion cylinder through a port that is separate from the air inlet passage. Thus the fuel does not premix with the incoming air, thereby allowing more precise control of the amount of fuel supplied to the cylinder and the point during the piston stroke at which the fuel is injected. Specifically, when the engine operates at higher speeds or higher loads, fuel injection occurs during the intake stroke which optimizes combustion under those conditions. During normal driving conditions, fuel injection happens at a latter stage of the compression stroke and provides an ultra-lean air to fuel ratio for relatively low fuel consumption. Because the fuel may be injected while high compression pressure exists in the cylinder, gasoline direct injection requires that the fuel be supplied to the injector valve at a relatively high pressure, for example 100 times that used in multi-port injection systems.
There are periods when all of the injector valves are closed and thus the gasoline in the conduit, known as the fuel supply rail, between the outlet passage of the fuel pump and cylinders has no place to go. This has not presented a significant problem in prior fuel systems that operated at lower pressure. However, at the significantly greater pressure of the gasoline direct injection system, the fuel system components down stream of the fuel pump must be capable of withstanding that pressure. In addition, a very high back pressure load occurs at the fuel pump at those times.
Therefore it is desirable to provide a mechanism for maintaining a consistent pressure level in the section of the fuel system that is downstream of the fuel pump outlet passage even as the injector valves open and close.
The present electrohydraulic flow control valve is intended to be connected to the high pressure side of a pump from which fuel is furnished to the injectors for the engine cylinders. This flow control valve provides a path through which high pressure fuel travels back to the low pressure line from the fuel tank thereby maintaining consistent pressure in the fuel supply rail. The flow control valve is designed for high speed operation. This is accomplished by an electromagnetic actuator that has components fabricated from a soft magnetic composite material. This composite material provides a non-electrically conductive path for the magnetic flux which reduces the eddy currents that otherwise would slow build-up of the magnetic flux and thus the speed of the actuator. Another factor enhancing performance of the flow control valve is that the armature of the electromagnetic actuator does not come into contact with the fuel flowing through the valve. Thus the armature motion encounters a lower fluidic resistance of air, as compared to liquid fuel.
The flow control valve includes a valve stem with a bore having a valve seat at one end. An inlet port in the valve stem provides an fluid path between the fuel rail and the bore. A valve element is located within the bore and selectively engages the valve seat to control flow of fluid between the inlet passage and outlet passages. The valve element has an exterior groove in communication with the inlet port. The exterior groove has first surface proximate to the valve seat and a second surface remote from the valve seat. Because the first surface is larger than the second surface, pressure in the groove tends to bias the valve element away from the valve seat, that is into an open position.
The electromagnetic actuator is operatively coupled to move the valve element with respect to the valve seat.